Research Journal of Applied Sciences, Engineering and Technology 7(18): 3709-3715, 2014
ISSN: 2040-7459; e-ISSN: 2040-7467
© Maxwell Scientific Organization, 2014
Submitted: June 28, 2013
Accepted: July 08, 2013
Published: May 10, 2014
Effects of Plant Species on Methane and Nitrous Oxide Emissions from Constructed
Wetlands Treating Municipal Wastewater
1, 2
Sukanda Chuersuwan, 1Pongthep Suwanvaree and 3Nares Chuersuwan
School of Environmental Biology, Institute of Science, Suranaree University of Technology, 111
University Ave., Muang District, Nakhon Ratchasima 30000, Thailand
2
Department of Water Resources, Bureau of Research Development and Hydrology,
Rama VI Road, Phayathai, Bangkok 10400, Thailand
3
School of Environmental Health, Suranaree University of Technology, 111 University Ave.,
Muang District, Nakhon Ratchasima 30000, Thailand
1
Abstract: This study was conducted to quantify emissions of greenhouse gases (GHGs), methane (CH 4 ) and
Nitrous Oxide (N 2 O), from free water surface constructed wetlands used for domestic wastewater treatment. All
constructed wetlands were monoculture and each plot was planted with Phragmites sp., Cyperus sp., or Canna sp.
The average CH 4 and N 2 O emissions were in the range of 5.9-11.2 and 0.9-1.8 g/m2/h, respectively. Seasonal
fluctuations of CH 4 and N 2 O emissions were observed. The highest fluxes of both GHGs occurred during hot rainy
season (July-October) followed by summer and the lowest found in cool season. The mean of CH 4 and N 2 O
emissions from different plants species were significantly different (p<0.05). Average CH 4 emissions from
constructed wetlands planted with Phragmites sp., Cyperus sp. and Canna sp. were 11.2, 6.0 and 5.9 mg/m2/h,
respectively, while mean N 2 O emissions were 0.9, 1.0 and 1.8 mg/m2/h, respectively. Calculated of Global
Warming Potential (GWP) found that GWP of CH 4 and N 2 O flux from constructed wetlands planted with Cyperus
sp., was the highest (669 mg CO 2 equivalent/m2/h), followed by Phragmite sp., (524 mg CO 2 equivalent/m2/h) and
Canna sp., (434 mg CO 2 equivalent/m2/h), respectively. These results suggested that municipal wastewater
treatment by constructed wetlands planted with Canna sp. and Phragmite sp., had potential of lower GHGs
emissions into the atmosphere and Phragmite sp., provided the highest removal rate of Biochemical Oxygen
Demand (BOD) and Chemical Oxygen Demand (COD).
Keywords: Constructed wetlands, methane, nitrous oxide, plant species, wastewater treatment
INTRODUCTION
Constructed Wetlands (CWs) systems are
combinations of natural wetlands and conventional
wastewater treatment processes and are constructed in
order to reduce input of nutrients and organic pollutants
to water bodies. Constructed wetland systems, a costeffective alternative, apply various technological
designs, using natural wetland processes, associated
with wetland hydrology, soils, microbes and plants
(Kadlec and Wallace, 2009; Casselles-Osorio et al.,
2011). Tropical countries, like Thailand, could have a
great benefit of wastewater treatment by constructed
wetlands. When constructed wetlands are used for
purification of wastewater, the productivity of the
ecosystem could increase as well as the production of
greenhouse gases (GHGs), which are by-or endproducts of microbial decomposition processes
(Inamori et al., 2007; Wang et al., 2008; Liu et al.,
2009; Wu et al., 2009). Constructed wetlands,
therefore, can be sources of important greenhouse
gases.
In constructed wetland microcosm, soil-plant is a
highly complex environmental system that acts as a
reservoir for microorganisms with their activity varying
over space and time. Plants release root exudation,
which easily decomposable and preferentially used by
microorganisms, increased carbon input into the system
(Tanner, 2001). Microbial growth in wetlands soil has
been believed to depend upon the plant species and
substrate. Furthermore, many species of emergent
plants CWs possess a convective flow mechanism when
oxygen is transported to the roots and gaseous
microbial by-products are emitted from plant roots to
the atmosphere (Brix, 1989; Brix et al., 1996). The
transport of gases by the convective mechanism is
faster than diffusion through water. The presence of
plants in constructed wetland system may increase gas
emissions from the soil. Therefore, plant species could
affect microbial ecology and gas emission from
treatment processes.
Although constructed wetlands can be beneficial
for wastewater treatment they may have an unfavorable
environmental impact by increasing the fluxes of
Corresponding Author: Sukanda Chuersuwan, School of Environmental Biology, Institute of Science, Suranaree University of
Technology, 111 University Ave., Muang District, Nakhon Ratchasima 30000, Thailand
3709
Res. J. App. Sci. Eng. Technol., 7(18): 3709-3715, 2014
greenhouse gases to the atmosphere. Thus, objectives of
this study were:
•
•
•
To quantify CH 4 and N 2 O emissions from
wastewater treatment constructed wetlands
To estimate seasonal fluctuations of CH 4 and N 2 O
emissions from wastewater treatment constructed
wetlands
To investigate the effect of plant species on CH 4
and N 2 O emissions
MATERIALS AND METHODS
Study site: The experimental scale of constructed
wetlands was built outdoor at Suranaree University of
Technology, Nakhon Ratchasima Province in
northeastern Thailand (Fig. 1). The geo-location of the
study area is 177879N and 1648339E. The region has
three-season monsoonal climate, with a relatively cool
dry season from November to late February, followed
by a hot dry season from March to June and then a hot
rainy season from July to October (TMD, 2012).
The experiment was employed on a regime of free
water surface flow constructed wetland. Eight
constructed wetlands with identical dimensions were
built based primarily on criteria of Aspect Ratio (AR)
or length to width of 4:1 to minimize short circuiting
and force the flow to move closely to plug flow
hydraulic regime (U.S.EPA, 2000). Each wetland had
the dimension of 2.0×0.5×0.8 m (length×width×depth).
Brick, cement and mortar were the materials used for
the construction of the constructed wetlands. Permanent
transparent roof made from clear plastic was also
constructed to prevent rain getting into the experiment
setup and allow direct sun light exposure. Three
emergent plants were used. All constructed wetlands
were monoculture with Phragmites sp., Cyperus sp. and
Canna sp. Each had two replicate cells.
The compositions of synthetic domestic wastewater
consisted of glucose, FeCl 3 , NaHCO 3 , KH 2 PO 4 ,
MgSO 4 •7H 2 O and urea (Sirianuntapiboon and Tondee,
2000), similar to the domestic wastewater from
Thailand's Housing Estates. The concentration of each
component is described below:
Glucose
190 mg/L
6.7 mg/L
NaHCO 3
MgSO 4 •7H 2 O 3.9 mg/L
FeCl 3
KH 2 PO 4
Urea
0.31 mg/L
6.0 mg/L
9.0 mg/L
Synthetic domestic wastewater was fed daily into
the constructed wetlands using gravimetric flow and the
flow was controlled by needle valves. The
characteristics of the prepared synthetic wastewater are
shown in Table 1.
Fig. 1: Map of study area in northeastern Thailand
Table 1: Characteristics of synthetic wastewater
Parameter
Range (mg/L)
BOD
115-235
COD
17-23
TP
0.03-0.33
TKN
0.28-0.35
Avg.: Average
from June 2010 to May 2011. The measurements of
GHGs fluxes were conducted between 09:00 and 15:00
periods. Gas emissions were measured using a static
chamber method described by Hutchinson and Mosier
(1981). The chambers consist of two parts. The upper
part was constructed from 3.0 mm clear acrylic sheet
and made gas-tight by heated glue doubling with silicon
sealant. The chamber included two gas sampling points,
a thermometer and a fan. Size of the acrylic chamber
was 0.25×0.25×1.5 m (width×length×height). A small
electronic fan was installed to ensure a thorough gas
mixing inside the chamber during the measurement.
The bottom part was made from aluminum rod. This
frame was used as a base for the upper part. Four-side
groove was made with 4.0 mm trench to accommodate
the 3.0 mm acrylic chamber during the gas sampling.
The aluminum frame was firmly inserted into the top
soil overnight prior the measurement. During the
measurements, the chamber was placed on top of the
aluminum frame. In each constructed wetlands, three
chambers were installed at the inlet, middle and outlet.
Gas flux measurements were performed at these three
sampling locations. The acrylic chambers were placed
on the aluminum bases and gas measurements began at
0, 15, 30 and 45 min intervals. Soil temperature at the
5-cm depth was also monitored, whereas soil pH, soil
ORP (at 5-cm depth) were measures by pH/ORP
device.
Methane (CH 4 ) and nitrous oxide (N 2 O) samples
were collected from the chambers and were analyzed
later in laboratory with Gas Chromatography (GC)
R
Gas flux measurement and analysis: Gases emissions
from the constructed wetlands were sampled monthly
Avg. (mg/L)
163
20
0.14
0.32
3710
R
R
R
Res. J. App. Sci. Eng. Technol., 7(18): 3709-3715, 2014
where,
E = Emission on the aerial basis (mg/m2/h)
X = Gas concentration increase in chamber (ppm/h)
h = Height of chamber (m)
M = Molecular weight
R = Gas constant = 0.0821 (atm/K/mol)
T = Absolute temperature (K)
Air pressure = 1 atm
P
Fig. 2: Linear relationship of greenhouse gas flux response
with time
instrument. Gas samples were taken from each chamber
with polypropylene syringes and transferred to
evacuated glass vial. Air inside the glass vials were
evacuated creating negative pressure prior to sampling.
Vials were overfilled in order to minimize potential
diffusion across the septa. All the samples were labeled
and kept cool in ice-packed cooler immediately after
the sampling. Then, the samples were transport to a
freezer, <4°C, waiting for later GC analysis.
Methane gas samples were analyzed in a laboratory
using a gas chromatograph (Agilent GC 6890, USA)
equipped with a flame ionization detector, a Poraplot Q
capillary column (0.32 mm ID×10 m). Column, injector
and detector temperatures were set at 40, 250 and
300°C, respectively, with split ratio 0.7:1 and split flow
15.0 mL/min. Nitrogen was use as carrier and flow rate
of 20 mL/min was maintained during analysis.
Nitrous oxide concentrations were determined
using a gas chromatograph (Agilent GC 6890, USA)
equipped with a 0.53 mm ID×15 m HP-Plot Q column
and a Micro Electron Capture Detector (µECD). The
temperatures of µECD and the column were set at 300
and 180°C, respectively. Nitrogen was supplied as the
carrier gas at a flow rate of 15 mL/min. Data were
analyzed by Agilent Chemstation A0803 software
(Agilent, USA). The concentrations of methane and
nitrous oxide in gas samples were extrapolated by
comparing chromatogram (peak area) of gas sample
with standard gases (Air Liquid, Ltd. and Scott
Specialty Gases, UK).
Gas emission rates were calculated based on the
gas and time linear relationship (Fig. 2). Gas
concentrations for each sample were plotted against
sampling time. Gas emission rate (ppm/h) was
converted to flux rates (mg/m2/h) and corrected for
chamber volume and temperature (Healy et al., 1996).
If the increase/decrease in the gas concentration was
non-linear (r2<0.85), the measurement was rejected
(Altor and Mitsch, 2006). Gas flux (mg/m2/h) was
calculated by the following equation:
E=
XhM
RT
P
Wastewater analysis: Daily wastewater samples were
collected from the influent and effluent points and
analyzed for Biochemical Oxygen Demand (BOD) until
the steady-state conditions were reached. After the
steady-state conditions have achieved, monthly
analyses were performed on influent and effluent
samples for BOD, Chemical Oxygen Demand (COD),
ammonia nitrogen (NH 3 -N) and Total Phosphorus (TP).
All
samples
were analyzed according
to
the
standard methods (APHA-AWWA-WEF, 2005).
R
R
0T
0T
0T3
0T3
0T
0T
Data analysis: Statistical analysis was performed with
SPSS® and Microsoft Excel® for Windows®. All data
entering statistical comparisons were tested for
homogeneity of variance and normal distribution using
Levene and Kolmogorov-smirnov Test. If assumptions
were fulfilled, one-way ANOVA and LSD’s post hoc
test were carried out. Otherwise, non-parametric ChiSquare (χ2) Test (Kruskal Wallis) was used instead,
followed by Mann-Whitney as Post-hoc test. In all
analysis, p<0.05 was considered as a significance level.
P
P
P
P
P
P
0T
P
P
0T
RESULTS
Constructed wetlands performance in wastewater
treatment: Average removal rates of BOD, COD,
NH 3 -N and TP were in the ranges of 57-70%, 51-67%,
25-43% and 39-45%, respectively (Table 2). Similar
removal rate of BOD was reported by Coleman et al.
(2001) that used Typha latifolia in constructed
wetlands. Higher removal rate of COD was found in
constructed wetlands planted with Eriochloa aristata
and Eleocharis mutate in Columbia reported by
Caselles-Osorio et al. (2010) at about 75%. In this
present study, the removal efficiencies varied in
constructed wetland units with different plants species.
High removal rate of BOD occurred in the units planted
with Phragmite sp., while low removal rate occurred in
Canna sp. The highest COD removal rate found in the
unit planted with Phragmite sp., while removal rate was
lowest in Cyperus sp. NH 3 -N was removed in the unit
planted with Canna sp., more effectively than
Phragmite sp. Total phosphorus removal rate was high
in the unit planted with Canna sp., while the rate was
lower in the units planted with Cyperus sp. Statistical
analyses of removal efficiency by one-way ANOVA
followed by LSD’s post hoc test indicated that average
removal rates of BOD, COD and NH 3 were
significantly different for all plant species (Table 3).
R
R
R
R
R
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Res. J. App. Sci. Eng. Technol., 7(18): 3709-3715, 2014
Table 2: Pollutants removal rates in constructed wetlands with different plant species
Pollutants removal rates (%)
----------------------------------------------------------------------------------------------------------------------Pollutant
Plant species
N
Mean
S.D.
Min.
Max.
BOD
Phragmite sp.
12
69.97
9.26
54.8
81.9
Canna sp.
12
56.85
8.45
43.4
68.7
Cyperus sp.
12
59.53
7.83
46.8
68.4
Total
36
62.11
10.08
43.4
81.9
COD
Phragmite sp.
12
67.17
5.54
58.2
75.0
Canna sp.
12
58.83
7.91
45.8
70.8
Cyperus sp.
12
50.71
8.41
37.4
64.6
Total
36
58.90
9.90
37.4
75.0
NH 3 -N
Phragmite sp.
12
25.24
7.44
9.6
36.3
Canna sp.
12
42.52
8.08
29.3
59.8
Cyperus sp.
12
41.13
9.94
28.6
59.9
Total
36
36.30
11.50
9.6
59.9
TP
Phragmite sp.
12
40.16
13.09
22.2
57.4
Canna sp.
12
45.23
20.09
19.8
78.6
Cyperus sp.
12
39.05
14.97
19.8
67.9
Total
36
41.48
16.08
19.8
78.6
S.D.: Standard deviation; Min.: Minimum; Max.: Maximum
Table 3: Comparison of pollutants removal rates among constructed wetlands with different plant species by one-way ANOVA
Pollutant CW
S.S.
df
M.S.
F
BOD
Between groups
1152.92
2
576.46
7.914
Within groups
2403.82
33
72.84
Total
3556.74
35
COD
Between groups
1626.85
2
813.42
14.875
Within groups
1804.62
33
54.69
Total
3431.46
35
NH 3 -N
Between groups
2212.44
2
1106.22
15.111
Within groups
2415.75
33
73.20
Total
4628.19
35
TP
Between groups
260.97
2
130.48
0.490
Within groups
8788.59
33
266.32
Total
9049.56
35
**: Significant at the 0.01 level; S.S.: Sum of square; M.S.: Mean square
Table 4: Seasonal variation of CH 4 and N 2 O emission from
constructed wetland with different plant species
CH 4 emission (mg/m2/h)
----------------------------------Mean
S.D.
Plant-season
Phragmite sp.
Hot rainy
19.88
Cool
3.92
Summer
6.29
Canna sp.
Hot rainy
10.29
Cool
2.40
Summer
3.17
Cyperus sp.
Hot rainy
10.83
Cool
2.65
Summer
2.12
S.D.: Standard deviation
N 2 O emission (mg/m2/h)
-----------------------------Mean
S.D.
16.23
3.32
4.42
1.32
0.32
0.90
1.15
0.12
0.89
7.67
2.48
2.72
1.41
0.31
1.42
1.19
0.14
1.26
10.58
2.07
1.47
2.60
0.32
2.46
2.44
0.12
1.71
Seasonal variation of environmental factors in
constructed wetlands: Monthly average of air
temperature reached maximum in September (36.7°C)
while the lowest mean was found in March (24.7°C). It
should be noted that lower air temperature in March
was unusual in the area of northeastern Thailand but it
occurred in March 2011 during the experiment. Soil
temperatures at all constructed wetlands were measured
at 5 cm depth. The graphic shown in Fig. 3 illustrates
that soil temperatures were in the range of 20-29°C,
which was in optimum range for plants and
microorganisms to grow (Iasur-Kruh et al., 2010) and
narrowly changed during three seasons. Soil
temperature peaked in December with the average of
29°C and reached its minimum value in January
Sig.
0.002**
0.000**
0.000**
0.617
(19.9°C) before it rise again in summer season (MarchJune).
Average soil pH during the experiments ranged
between 6.7 and 8.0, in different constructed wetlands.
However, soil pH remained in the optimum range for
methanogenic bacteria (Iasur-Kruh et al., 2010).
There were differences in soil Oxidation-Reduction
Potential (ORP) across the seasons. The lowest soil
ORP occurred in January with the average of -258±5
mV whereas the highest soil ORP occurred in May with
the average of -127±6 mV.
Seasonal variation of CH 4 gases emissions from
constructed wetlands: Methane emissions from all
constructed wetlands observed during August and
September were noticeable higher than those in other
months (Fig. 3). The highest CH 4 emissions from all
constructed wetlands with different plants occurred in
September with the average of 58.3, 44.9 and 21.6
mg/m2/h for Phragmite sp., Canna sp. and Cyperus sp.,
respectively. The lowest CH 4 emissions occurred
during December and March. CH 4 emissions from
constructed wetlands planted with Phragmite sp. and
Canna sp., were lowest in March with the average of
2.4 and 1.1 mg/m2/h, respectively, whereas low CH 4
emissions from Cyperus sp., occurred in December
with the average of 0.9 mg/m2/h. When seasonal
variation was taken into account, CH 4 emissions from
all constructed wetlands were highest in hot rainy
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Res. J. App. Sci. Eng. Technol., 7(18): 3709-3715, 2014
Fig. 3: Seasonal variation of CH 4 emission from constructed wetland planted with Phragmite sp., Canna sp. and Cyperus sp.,
Fig. 4: Seasonal variation of N 2 O emission from constructed wetland planted with Phragmite sp., Canna sp. and Cyperus sp.,
season (July-October) with the average of 10.3-19.9
mg/m2/h and lower in summer season (March-June)
with the average of 2.1-6.3 mg/m2/h and cool season
(November-February) with the average of 2.4-3.9
mg/m2/h. The CH 4 emission was lower in summer
season that may because the lower air temperature in
March was unusually low indicating that local climate
fluctuation was influence CH 4 emissions from
constructed wetlands in the area. Seasonal variation of
CH 4 emissions is summarized in Table 4.
Seasonal variations of N 2 O gases emissions from
constructed wetlands: High Nitrous oxide emissions
from all constructed wetlands were found during April
and October (Fig. 4). The highest N 2 O emissions from
constructed wetlands planted with Phragmite sp., were
highest in June with the average of 3.6 mg/m2/h while
high emissions from Canna sp. and Cyperus sp.,
occurred in April with the average of 2.9 and 3.7
mg/m2/h, respectively. The lowest N 2 O emission from
constructed wetlands planted with Phragmite sp. and
Canna sp., occurred in November with the average of
0.3 and 0.2 mg/m2/h, respectively. Low N 2 O emissions
from Cyperus sp., occurred in February with the
average of 0.3 mg/m2/h. When seasonal variation was
taken into account, N 2 O emission from all constructed
wetlands were highest in hot rainy season (JulyOctober) with the average of 1.3-2.6 mg/m2/h, followed
by summer season (March-June) with the average of
0.9-2.5 mg/m2/h and lowest in cool season (NovemberFebruary) with the average of 0.3 mg/m2/h.
Influence of plant species on CH 4 and N 2 O emissions:
Data on CH 4 and N 2 O emissions from seasonal study
were used to evaluate the influence of plant species
within constructed wetlands on greenhouse gas
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Res. J. App. Sci. Eng. Technol., 7(18): 3709-3715, 2014
Table 5: Comparison of CH 4 and N 2 O emission from constructed wetland with different plant species using chi-square (χ2) test (Kruskal Wallis)
Emission rate (mg/m2/h)
-----------------------------------------------------------------------------------------Asymp. Sig.
GHG/CW
N
Mean
S.D.
Min.
Max.
χ2
(2-tailed)
CH 4
Phragmite sp.
72
11.16
16.10
0.00
113.87
9.88
0.007**
Canna sp.
72
6.01
6.70
0.00
39.96
Cyperus sp.
72
5.92
9.82
0.00
71.56
N2O
Phragmite sp.
72
0.88
1.17
0.08
6.06
7.06
0.029*
Canna sp.
72
1.04
1.20
0.02
6.67
Cyperus sp.
72
1.80
2.06
0.03
7.32
*: Significant at the 0.05 level; **: Significant at the 0.01 level; S.D.: Standard deviation; Min.: Minimum; Max.: Maximum
emissions. Descriptive statistics for CH 4 and N 2 O
emissions are shown in Table 5. Data screening showed
that gas emissions were neither a normal distribution
nor homogeneity of variance. Thus, chi-square was
suitable for differentiating greenhouse gas fluxes among
different plant species within constructed wetlands. The
means of CH 4 and N 2 O emissions from different plants
species were compared by chi-square (χ2) test (Kruskal
Wallis). The results showed that the mean of CH 4 and
N 2 O emissions from different plants species were
significantly different (p<0.05). Constructed wetlands
planted with Phragmite sp., emitted the highest CH 4
with the average of 11.2 mg/m2/h but emitted the lowest
N 2 O with the average of 0.9 mg/m2/h. Constructed
wetlands planted with Cannas sp., emitted CH 4 and
N 2 O with the average of 6.0 and 1.0 mg/m2/h.
Constructed wetlands planted with Cyperus sp., emitted
CH 4 with the average of 5.9 and highest N 2 O with the
average of 1.8 mg/m2/h.
Estimated Global Warming Potential (GWP) of CH 4
and N 2 O emissions from constructed wetland
planted with different plants: Comparison of CH 4
and N 2 O characteristics in terms of Global Warming
Potential (GWP), were corresponded to the average
GWP of CH 4 and N 2 O at 23 and 296 times of CO 2 ,
respectively (IPCC, 2001). Our estimate showed that
the GWP of constructed wetlands planted with
Phragmite sp., had the average CH 4 and N 2 O
emissions about 11.2 and 0.9 mg/m2/h, respectively.
These numbers were about 258 and 266 mg CO 2
equivalent/m2/h (or 524 mg CO 2 equivalent/m2/h in
total). Constructed wetland planted with Canna sp., had
the average CH 4 and N 2 O emissions of 6.0 and 1.0
mg/m2/h, respectively, corresponded to the average
GWP of 138 and 296 mg CO 2 equivalent/m2/h, for CH 4
and N 2 O emissions, respectively (or 434 mg CO 2
equivalent/m2/h in total).
In the case of constructed wetland planted with
Cyperus sp., the average CH 4 and N 2 O emission were
5.9 and 1.8 mg/m2/h, respectively. Estimated mean
GWP of CH 4 and N 2 O emissions were 61 and 325 mg
CO 2 equivalent/m/h, respectively, or approximately
669 mg CO 2 equivalent/m2/h. Therefore, the results
indicated that estimated GWP of CH 4 and N 2 O
emissions from constructed wetland planted with
Cyperus sp., was the highest, followed by Phragmite
sp. and Canna sp., constructed wetlands, respectively.
DISCUSSION
Average CH 4 and N 2 O fluxes from wastewater
treatment constructed wetlands, planted with three
emergent plants, ranged between 5.9-11.2 and 0.9-1.8
mg/m2/h, respectively. The average fluxes were
comparable to those reported by Inamori et al. (2007)
which used experimental scale free water surface flow
constructed wetland treating non-point sewage at
Tsukuba, Japan. However, average N 2 O emission was
lower than the studies of 2.39 and 3.4 mg/m2/h reported
by Wu et al. (2009) and Inamori et al. (2007). Seasonal
fluctuations of CH 4 and N 2 O emissions were observed
in this present study. The average CH 4 and N 2 O
emissions were highest in hot rainy season, followed by
summer season and lowest in cool season. However, the
pattern of seasonal CH 4 and N 2 O emission variations
and their relations to environmental factors were not
obvious. These may because important environmental
factors such as soil temperature, soil pH and soil ORP
were in the optimum range for gas production and
changed in a narrow range during the experiment.
Additionally, CH 4 and N 2 O emissions were not the
result of one-factor action but of the interaction of more
biotic and abiotic factors.
Means of CH 4 and N 2 O emissions from different
plants species were significantly different (p<0.05).
Average CH 4 and N 2 O emission from constructed
wetlands planted with Phragmite sp., Cyperus sp. and
Canna sp., were 11.2, 6.0 and 5.9 mg/m2/h and 0.9, 1.0
and 1.8 mg/m2/h, respectively. Estimated GWP showed
that CH 4 and N 2 O emissions from constructed wetlands
planted with Cyperus sp., was highest (669 mg CO 2
equivalent/m2/h), followed by Phragmite sp., (524 mg
CO 2 equivalent/m2/h) and Canna sp., (434 mg CO 2
equivalent/m2/h), respectively.
For pollutant removal, it was found that
constructed wetland planted with different plants had
significantly different in efficiency of BOD, COD and
NH 3 -N removal although TP removal rates indicated no
significantly different. The constructed wetland planted
with Phragmite sp., had the highest removal rate of
BOD and COD but had lowest efficiency on NH 3 -N
removal. Cyperus sp., or Canna sp., had the higher
removal efficiency on NH 3 -N. Despite the benefit of
constructed wetlands on wastewater treatment, it is
important to considered by-product of constructed
wetlands in low carbon era. The use of Phragmite sp.,
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Res. J. App. Sci. Eng. Technol., 7(18): 3709-3715, 2014
should be of benefit in reducing GWP from these
greenhouse gases when it is used in constructed
wetlands for wastewater treatment.
ACKNOWLEDGMENT
This study was supported by Environmental
Biology Program, Institute of Science, Suranaree
University of Technology. The authors gratefully
acknowledge the support.
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